Autism spectrum disorders (ASD) are an etiologically heterogeneous set of neurodevelopmental disorders marked by social communication/interaction deficits and restricted/repetitive behaviors. Genetic studies have identified a strong heritable component, yet >80% of ASD remains idiopathic. Marked heterogeneity has slowed attempts to identify pathophysiology and related therapeutic targets. One promising strategy to reduce complexity is to focus on subgroups with a specific genetic etiology, such as ASD associated with germline heterozygous PTEN mutations (PTEN-ASD, who are always macrocephalic). In the last 4 years, we characterized cross-sectional neurobehavioral and neurocognitive differences among PTEN-ASD, those with PTEN mutations but no ASD (PTEN-no ASD) and macrocephalic ASD without PTEN mutations (Macro-ASD) and begun longitudinal data collection in individuals aged 3-21. We propose a natural history study of the neurophenotypic and molecular characteristics of PTEN-ASD with the goals of understanding risk management and treatment planning as well as identifying sensitive biomarkers for intervention studies. We will recruit 170 (70 from current cohort) individuals with PTEN-ASD, Macro-ASD, and PTEN no-ASD, and expanding recruitment to aged 18 months to 45 years. Data collected will include: (a) cancer occurrence, (b) autism and other behavioral symptoms, (c) neurocognitive profiles, (d) adaptive function, (e) genomic modifiers, (f) protein levels from PI3K/AKT/mTOR/S6K pathway, and (g) EEG, in order to: (Aim 1) Determine cross-sectional and longitudinal neurobehavioral and medical differences between PTEN-ASD and other groups in an expanded age range. This aim seeks to describe initial levels and longitudinal changes in cancer occurrence, behavioral signs/symptoms, and cognitive function in PTEN-ASD; (Aim 2) Identify EEG and molecular biomarkers specific to PTEN-ASD and those shared with other groups. This aim seeks to identify biomarkers that may be treatment targets in intervention studies; and (Aim 3) Develop a comprehensive, multi-level, longitudinal model of PTEN-ASD to inform future clinical trials and the development of consensus care guidelines. We will use data from Aims 1 and 2 and from TSC Associated Neuropsychiatric Disorders (TAND) Checklist (after validation). This first comprehensive longitudinal evaluation of the phenotypic and molecular characteristics of PTEN ASD, to identify specific molecular pathway and correlated neural abnormalities responsible for ASD symptoms in these individuals, which can be ably compared to TSC and PMS. It is a crucial next step toward the development of personalized genetic treatment approaches for PTEN-ASD. Prior to initiating further clinical trials, it will be critical to identify treatment targets at the molecular, neurophysiological, and behavioral levels.